UK-Cherub Forum
Cherub Chat => Tech Chat => Topic started by: PaulJ on May 04, 2012, 08:20:23 AM
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Has anyone successfully made any PBO rigging, doesn't seem that challenging to do.
Any idea where I would get some monofilament from.
How many fibres would I need to make a 3mm shroud
Any suggestions on how to get an even tension on all the fibres before adding the end fittings.
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We made some from some braided pbo which was a gift from marlow ropes. They were stiffer than SK78 but needed a jacket against the UV, so were v thin in the middle and therefore less actual use than the SK78.
Alex Vallings in NZ says he makes them by putting two screws the right distance apart and then winding and winding. Then he posts the long 'coil' up through some thin rope outer or pvc tube, and then dips the ends in pigmented epoxy.
We did not follow this route because of exactly what is concerning you: evening up the tension.
Thinking about it now, small thimbles at each end, and pretensioning it many times before epoxying the ends (and using flexible epoxy) might help.
I'd be really interested to see how you get on.
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where would you source the monfilament will? this is really interesting to me also
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Alex was suggesting we moved to carbon rod on the new rig.
Apparently the the idea is to make up "strings" from uni tow (toe). Even with normal resin these are then flexible, but you will not be coiling them in less tah n a 1-1.5m diameter (think Graham's pop up tent size). Obvious quesitons about what happens at shrouds, should we use a different resin and are we brave enough.
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Err yes what to do where they pass through the spreaders will need to be thought about.
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I have been thinking about the tension issue. I think if I use a fishing reel to spool the monofilament with the drag set reasonably low, plus a jockey weight (1 kg maybe) but not too heavy that it overcomes the reel drag. This would be set up at one end. I would then take a loop of filament, loop it round the far end thimble and release and repeat again and again. I should get in theory get a consistant tension (1 kg). Once complete I would then hang a big weight from one end and bounce it up and down to bed everything down, possibly leave it overnight as well. Once that is done, make a couple of temporary whippings to hold everything in place whilst I remove one of the thimbles to pass over shrink wrap tube or rope outer cover, re tension everything with the big weight again, apply heat to the shrink wrap, and whip the ends adjacent to the thimbles, cover the whipping and thimble in flexible epoxy, once that has gone off cover each end with a bigger shrink wrap tube. Install on the boat and go sailing.
Any ideas on where I can source the PBO monofilament from ?
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No idea of the source - Alex Vallings is the person to start with.
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id be happy to trial anything shroud like that people arent sure about on my boat as a test when i get back from minorca
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I used to do archery quite seriously and we used to make our own bow strings (out of materials such as Kevlar, Dyneema, Dacron etc) which you used to make by looping a single filament round a jig.
I've found a link to save a full explanation...
http://digital.cs.usu.edu/~watson/artemisiaca/bowstringhowto.htm
I don't really see why you couldn't do something similar on a larger scale for shrouds (maybe start at a set of lowers, and then work up to something longer) Once you have the string we always used to put in a number of twists and then wax them to bind the filaments together. You could do basic length tuning by twisting the string to make it shorter, or removing twists to make it longer. You could do this with PBO or Dyneema I reckon and it would be stronger as you wouldn't splice the ends in the same way as you do conventional rope.
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PBO yarn turned up yesterday. It is very UV sensitive so has to be kept in a black bag. I have made up a sample length about 500mm long, 3mm dia approx. will test it with the car and tree tonight. The detail is going to be key to a neat and reliable finish around the thimbles, the end whipping and thimbles will be encased in flexiable epoxy, the main stay is encased in shrink tubing with heat activated glue inside.
Going to make a forestay first and test it at Weston, then lowers and finally main shrouds when I am sure everything is ok.
Cost is approx £10 per metre including end fittings.
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Hi Paul,
When you do your test with the car and the tree. Why not connect a wire strop in line with the PBO test piece.
If the wire breaks first - great.
If the wire does not break the deformation of the wire thimbles would give a fair indication of the load applied compared to the deformation that we see on the boats.
Unless you happen to have a suitable load cell lurking in your garage.
I want to try and make some Carbon shrouds using standard thimbles but reckon that deformation of the thimble will initiate a failure and that the thimbles will need to be stiffened.
First though we needed to finish a few races. Exotic parts look like yet another way not to finish a race.
Clive.
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Load test carried out, put an unbelievable load into it, couldn't get the Loos gauge on it at all. Wasn't prepared to put any more load into it as the landrover in low range was beginning to object. So I think it's strong enough to put on the boat.
Need to look at how I whip the fibres together at the thimble as it showed signs of slipping slightly away from the thimble when under load.
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thats pretty cool, how many turns did you take/ how big a diameter was it?
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Not sure how many turns, just did some for the test piece, it came out about 2.5mm dia, this increases to about 3.5 with the heat shrink cover. Size not an issue for the forestay as it's inside the jib luff anyway, but I may have to look into a different shrink wrap for the shrouds to keep the windage down. 550mm length weighs 23g includng the thimbles, expect the forestay to weigh 150g, shrouds maybe a bit less.
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pretty fantastic, how musch do you reckon the finished forestay will cost you?
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The material costs have come to about £160, but I have enough of everything to make 2 complete sets at least, forestay, 2 shrouds and lowers, not going to make uppers as they are already dynema sk90
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Update - PBO forestay finally finished on Saturday morning prior to leaving for Weston, again tested with the tree and Landrover in low range, managed to deform a good sized shackle, it was sail tested on Tuesday in 20 knots of breeze and performed without a hitch, unfortunately the professionally made dyform shrouds failed, but that's another story
PBO forestay facts
Approx 5m long
Finished OD - approx 4mm
Component weight - approx
2 No. Stainless thimbles - 7g
PBO - 50g (44 yarns)
Heat shrink tape - 10g
Black polyester braid cover -15g
Heat shrink tubing - 5g
Flexible epoxy - 1g
Total weight - 90g
Current Dyform 3mm forestay - 400g
Total manufacture time 3 hours, the most time consuming part was winding the heat shrink tape. The orginal plan was to use adhesive heat shrink tubing but this weighed 13g/m so was rejected. The braided cover is a bit big and will be too high windage for shrouds, (fine for a forestay though as it inside the jib luff), so a smaller diameter needs to be sourced. Expected total rigging weight including forestay, shrouds and lowers, including shackles etc - 550g.
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very interesting, what price estimate have you come up for the whole rigging?
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If you scales are good I would be very interested in weight made, after first dunk and then a few months later.
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"On modern racing yachts Zylon is used for parts of the standing rigging. It is used as shrouds and stays, except the forestay due to torsion weakening the fiber"
Interesting what our friend wikipedia has to say about PBO
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could that be due to roller furlers? forgive me, i know knothing about yachts
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Good point, I was wondering where the torsion came from.
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This recent thread from the antipodean second-cousins might be of interest:
http://z10.invisionfree.com/12ft_skiffs/index.php?showtopic=508 (http://z10.invisionfree.com/12ft_skiffs/index.php?showtopic=508)